Candles generally include a wick embedded in a solid combustible material. The basic principle involved is the melting of the combustible material to produce a liquid, which is transported up the wick by capillary action and vaporizes/combusts in the flame of the candle. Wicks are usually made of woven cellulosic materials, such as cotton or paper. Moreover, candles are multiple use devices, i.e. they can be lit and extinguished over many cycles during the useful lifetime of the device.
Historically, candles have been produced from compositions containing predominately animal fats, such as tallow or natural waxes such as beeswax. Additional suitable waxes include petroleum waxes such as medium paraffin wax and microcrystalline paraffin wax that are derived from petroleum refining processes. The main advantages of petroleum products over tallow in candle compositions is that petroleum products have better control over the melting temperature range of the solid material as well as cost. This control is created by the blending of different molecular weight fractions of linear and non-linear alkane/alkene hydrocarbons. By appropriate blending, the candle material is a solid at ambient temperatures, but readily melts to form a liquid at elevated temperatures. In some cases, candles may contain lower molecular weight hydrocarbons which would be liquids at ambient temperatures, but the composite appears as a solid, due to molecular distribution among larger, higher melting temperature components. As such, predominately petroleum based candles exhibit an amorphous solid structure as opposed to a crystalline structure.
The solid structure of candles is important for both performance and aesthetics. The solid structure of a candle composition effects the burning characteristics of the candle and the appearance of the candle. Different types of candles have different requirements. For example, it is desirable for standalone candles (tapers, pillars, etc.) to be solid with a smooth, glossy appearance, without residual sticky/greasy feeling on the exterior.
Large candles produced predominately from petroleum products exhibit poor aesthetic properties. Petroleum waxes decrease in volume upon solidifying from a liquid melt (i.e. density of the solid is greater than the liquid). Most candles produced from petroleum products, such as 3-6 inch diameter pillar candles, tend to exhibit the formation of a concave surface or the formation of gaps or holes on the interior of the candle.
Candles produced from petroleum waxes additionally produce a black smoke upon burning and generally exhibit an unpleasant odor. Depending on the molecular weight distribution of paraffin, large molecular weight or more complex molecules do not combust as readily as smaller, simpler molecules, and therefore have the tendency to form significant amounts of soot. The black smoke of petroleum-based candles contains polycyclic aromatic hydrocarbons, metals, and sulfur compounds that may be carcinogenic and/or toxic. Burning these candles in an enclosed environment increases the concentrations of these compounds and could therefore increase the detrimental effects associated with these compounds.
The cost of using petroleum products in candles will likely increase due to the low supply and increasing demand. The production of petroleum waxes is being reduced because petroleum refining processes are constantly being improved to maximize quantities of short chain hydrocarbons and aromatic chemicals.
As a result, there is a need for a candle composition that minimizes the risk to human health upon burning, utilizes renewable resources while minimizing or eliminating use of petrochemical-derived products, and has a naturally pleasing odor. This invention addresses that need.